Bias Calculator

DANGER: LETHAL VOLTAGES PRESENT

Tube amplifiers operate using dangerous high-voltage direct current (DC) ranging from 300V to over 700V, which can store lethal charges in filter capacitors even when unplugged. Always safely discharge capacitors and measure 0V DC before touching internal circuitry. If you are not trained in high-voltage amplifier service, take your amp to a qualified technician.

Vacuum Tube Bias & Dissipation Calculator

Reference tool based on Rob Robinette's tube biasing equations. Enter your tube type and measured plate-to-cathode voltage to run calculations across all three modules.

Step 1: Global Inputs (Required for all calculators)

Measured directly from Plate pin to Cathode pin.

Module 1: Target Bias Current Targets

Amplifier Class & Topology Cool Average Max Safe Limit
Class AB Fixed Bias -- mA (50%) -- mA (60%) -- mA (70%)
Class A Fixed Bias -- mA (70%) -- mA (80%) -- mA (90%)
Cathode Bias -- mA (85%) -- mA (95%) -- mA (100%)

Module 2: Tube Dissipation via Cathode Resistor Voltage Drop

Automatically subtracts ~5.5% estimated screen current for pentodes/tetrodes.

Total Cathode Current -- mA
Plate Current Per Tube -- mA
Plate Dissipation Per Tube -- W -- % of Max

Module 3: Tube Dissipation via Direct Plate Current

Use when directly measuring plate current (e.g., Output Transformer Shunt Method or Bias Probe).

Calculated Plate Dissipation -- W
Operating Dissipation Percentage -- % --